A hemoglobin derivative, namely, hemoglobin A1c, can be detected in a normal blood glucose level, from which the effect on a blood sugar level (change) by meal is eliminated. Accordingly, hemoglobin A1c is an item frequently measured for early detection of a lifestyle-related disease. Hemoglobin A1c consists of hemoglobin (contained in a red blood cell) and glucose bound to the hemoglobin and is numerically expressed by a ratio (%) of hemoglobin A1c relative to hemoglobin. Therefore, to obtain the ratio of hemoglobin A1c, it is necessary to measure hemoglobin and hemoglobin A1c, separately. Hemoglobin is measured by a method of using light absorption intrinsic of hemoglobin and generally measured near at a wavelength of 415 nm or 540 nm. As a method for measuring hemoglobin near at a wavelength of 540 nm, a cyanmethemoglobin method and an SLS hemoglobin method are widely known. Furthermore, hemoglobin A1c is immunologically measured. For this, hemoglobin has to be taken out of a red blood cell by hemolysis of blood in a sample and the tertiary structure of hemoglobin is changed in order to determine whether the hemoglobin taken out is non-glycated hemoglobin or hemoglobin A1c, thereby exposing a glycated site of hemoglobin out of the tertiary structure. This is called denaturation.
Furthermore, the glycated site is allowed to react with an antibody specifically recognizing the glycated site. In this way, the amount of hemoglobin A1c can be immunologically determined.
Note that, as a prior-art document of the present invention, International Publication WO2006/112339 (WO2006/112339A1) is already published. In the publication, a denaturation method for measuring hemoglobin A1c is also disclosed. This method is directed to a method for measuring a hemoglobin derivative by treating a sample containing a blood component with a nonionic surfactant and an oxidizing agent to denature hemoglobin in the sample.
Furthermore, in clinical tests recently performed, various examination methods have been used in order to examine a stage of disease progression. A large scale automatic analyzer, which is capable of quantitatively determining various components in a biological sample, by reacting the biological sample such as blood with analysis reagents, has been used in practice and come to be an indispensable apparatus in the medical field. In the circumstances, lately, it has been commercially desired to develop a more accurate and more universal analyzer including an analysis method reduced in cost, amount of a sample solution, measurement time and size, and enabling simultaneous measurement of many items.
Of the analyzers and analysis methods more universally used, a measurement principle based on an antigen-antibody reaction is generally known, including immunoassays such as immunonephelometry, latex immunoagglutination method, immunoagglutination inhibition method, latex immunoagglutination inhibition method, fluoroimmunoassay, chemiluminescent immunoassay, electrochemical immunoassay, fluorescence polarization immunoassay, and immunochromatography.
In the immunoassay based on a particle agglutination reaction, a specific component in a biological sample is qualitatively and quantitatively measured and determined based on the presence or absence of agglutination of a free anti-analyte antibody or an anti-analyte antibody bound to a water suspensible particle and the degree of agglutination thereof. The water suspensible particle most generally used is a particle called a latex particle.
Of the immunoassays based on the particle agglutination reaction, a measuring method using an immunological particle agglutination inhibition reaction is known. When an anti-analyte antibody and an agglutinating reagent specific to the antibody are mixed, the agglutinating reagent recognizes the anti-analyte antibody to cause agglutination. However, if an analysis object is present in this system, the agglutination is inhibited. Therefore, the analysis-object can be quantitatively detected by optically measuring or counting the degree of agglutination. This measuring method is widely applicable to various types of analysis-objects. In the agglutination reaction, the concentration of an agglutinating reagent has a large effect upon the reaction.
Note that, as an agglutinating reagent used in immunoassay informed in prior-art documents, a ligand-polymer complex is known and generally frequently used (for example, see Japanese Patent Application Laid-Open No. 1-155272). More specifically, the document discloses a ligand-polymer complex, which is an agglutinating reagent for measuring a specific component, particularly, hemoglobin A1c, in a biological sample. The ligand-polymer complex described has a ligand, which is covalently bonded on a polymer material such as polyaspartic acid. FIG. 14 shows an image of a conventional agglutinating reagent formed of a ligand-polymer complex. The conventional agglutinating reagent 4 is composed of a polypeptide (carrier) 5, a linker 2 and a ligand 3 and produced by binding the polypeptide (carrier) 5 to the ligand 3 via the linker 2.    Patent Document 1: International Publication WO2006/112339    Patent Document 2: Japanese Patent Application Laid-Open No. 1-155272